Various amorphous polyamide compositions and utility thereof in a wide range of applications are well known. Such compositions are generally characterized by a high degree of transparency and lack of a sharply defined melting point. Applications for such compositions include films, sheets, laminates and molded articles. A disadvantage of some of these compositions is their relatively poor thermal properties which limits their utility to relatively low temperature applications.
An example of such a composition, disclosed in U.S. Pat. Nos. 2,715,620 and 2,742,496, is a polyamide of isophthalic acid and hexamethylenediamine. As reported in U.S. Pat. No. 4,250,297, however, such compositions have poor dimensional stability at elevated temperatures. That patent proposed to overcome such difficulties by replacing part of the hexamethylenediamine with an isomer mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine.
Amorphous polyamides based on terephthalic acid and isophthalic acid or their derivatives and hexamethylenediamine also are known as reported in U.S. Pat. No. 3,379,695 and U.S. Pat. No. 3,475,387. While such compositions exhibit improved heat deflection temperatures relative to the isophthalic acid and hexamethylenediamine polyamides, transparency of articles prepared from the compositions suffers and crystallization of the polymer can occur during use of the articles at elevated temperatures if the mole ratio of isophthalic acid to terephthalic acid is too low.
U.S. Pat. No. 2,766,222 discloses transparent compositions prepared from isophthalic acid or isophthalic acid/terephthalic acid mixtures and metaxylylenediamine and that such compositions are suitable for production of molded articles of high transparency, good heat and chemical resistance and excellent tensile and impact strengths. Softening points of 150.degree.-170.degree. C. for such compositions are reported in the examples. It also is disclosed that transparency of the compositions suffers if greater than about 40 mol % isophthalic acid is replaced with terephthalic acid.
U.S. Pat. No. 4,018,746 also is directed to transparent metaxylylenediamine-based compositions, disclosing polyamides prepared from a mixture of straight chain aliphatic diamines of 4-20 carbon atoms and metaxylylenediamine or a mixture of metaxylylenediamine and paraxylylenediamine and a mixture of a saturated aliphatic dicarboxylic acid of 5-20 carbon atoms and at least one aromatic dicarboxylic acid selected from terephthalic acid and isophthalic acid. Aliphatic diamine content of the diamine mixture is said to range from 5-90 mole % and aliphatic acid content of the acid mixture is said to range from 10-90 mol %. The polyamides are said to be useful in preparation of transparent articles such as sheets, plates, tubes, wire coverings and injection molded technical parts.
Utility of metaxylylenediamine group-containing polyamides in molded containers and vessels is disclosed in U.S. Pat. No. 4,398,642 directed to a multi-ply vessel comprising an inner layer of polyester resin, a middle layer composed of a metaxylylene group-containing polyamide resin and an outer layer composed of a synthetic resin having impermeability to moisture. The metaxylylene group-containing polyamide middle layer is said to provide gas barrier properties. However, the glass transition temperature of the metaxylylene polyamide is about 80.degree. C., such that vessels prepared therefrom are susceptible to deformation at elevated temperatures including those to which the vessels may be exposed during hot filling processes.
U.S. Pat. No. 4,535,901 discloses a multi-ply vessel comprising an odd number of layers with the innermost and outermost layers of polyester resin, and at least one middle layer composed of a metaxylylene group-containing polyamide. The middle layer is covered completely by both inner and outer layers to provide good water resistance, high chemical resistance and high hygienic qualities.
It also is known that water absorption lowers the glass transition temperature, Tg, and the crystallization temperature of non-oriented metaxylylene polyamide resin. This effect is observed as a haze in the nonoriented neck portions of multilayer containers having such resins as the inner gas barrier layer. U.S. Pat. No. 4,501,781 discloses that a gap may form between the inner surface layer and the intermediate layer resulting in a decrease of transparency of the container. The patent discloses the use of a mixture of polyethylene terephthalate resin and a xylylene group-containing polyamide resin.
Japanese Patent Applications 60-232,952, 60-238,355 and 60-240,452 disclose copolymers of metaxylylenediamine with adipic acid and isophtalic acid containing 30 to 100% isophthalic acid and polyester laminated moldings consisting of a copolymer layer and a polyethylene terephthalate layer.
U.S. Pat. No. 4,728,549 discloses a biaxially oriented multilayered container comprising a wall portion consisting of at least two metaxylylene group-containing polyamide resin layers and one more polyethylene terephthalate layer than the number of metaxylylene group-containing polyamide layers with the terminal portion of the mouth opening being polyethylene terephthalate.
U.S. Pat. No. 4,800,129 discloses thermoformed multilayer structures comprising at least a first and a second layer, the first layer comprising a blend of amorphous polyamides having a Tg greater than about 120.degree. C. and one or more semicrystalline aliphatic polyamide and the second layer comprising a structural thermoplastic resin.
European Patent Application 0 212 339 discloses a method for making a hollow two-layer blow-molded bottle having one layer formed of a biaxially oriented polyethylene terephthalate resin and a second layer formed of a mixture of polyethylene terephthalate resin and 5 to 50 percent by weight of a xylene derivative polyamide resin.
European Patent Application 0 186 154 discloses a nine-layer parison, process for its production and a multilayer container produced from the parison wherein the nine-layer structure is composed of two outside layers and one central layer of polyethylene terephthalate (PET) and two interlayers of a metaxylylenediamine (MXDA) nylon with four adhesive layers of a thermoplastic adhesive resin being positioned between the PET layers and the MXDA nylon layers. This process requires adhesive layers between the PET and MXDA nylon layers.
European Patent Application 0 288 972 discloses a multilayered structure having at least one layer of a copolyamide composed of 55 to 70 mol % of an aliphatic dicarboxylic acid component and 45 to 30 mol % of an aromatic dicarboxylic acid component and a diamine component consisting substantially of metaxylylenediamine. The copolyamides of this patent have relatively high levels of an aliphatic dicarboxylic acid such as adipic acid and use metaxylylenediamine as the diamine component.
U.S. Pat. No. 4,133,802 discloses a biaxially drawn film of a polyamide containing a metaxylylene group which has excellent mechanical and physical properties including a high gas barrier property.
While these patents and publications disclose various amorphous polyamides and properties thereof, there remains a need for polyamide compositions having a desirable balance of properties, including ease of melt processing, sufficiently high glass transition temperature for use of articles fabricated from the compositions at elevated temperatures, good transparency and resistance to hazing and good oxygen barrier properties.
An object of the present invention is to provide improved polyamide compositions.
A further object is to provide a polyamide composition which exhibits improved gas barrier properties, resistance to whitening upon exposure to moisture and ease of processing.
A still further object of the present invention is to provide metaxylylenediamine-containing polyamides for use as the polyamide compositions and for use as a blend component for miscible polyamide blends that make up the improved polyamide compositions.
These and other objects and advantages of the present invention will be apparent to those skilled in the art from the following description.
We have now found that the objects of this invention can be attained by providing polyamide compositions comprising recurring hexamethylene and metaxylylene isophthalamide, adipamide and, optionally, terephthalamide units in proportions such that a high degree of transparency and resistance to whitening and glass transition temperatures, Tgs, of at least about 90.degree. C. are obtained. Advantageously, such polyamide compositions can be prepared directly by copolymerization of suitable starting materials or by blending polyamide homopolymers or copolymers to achieve the desired component proportions. Such polyamide compositions exhibit single Tgs. The compositions are well suited for use in the manufacture of a wide range of fabricated articles, such as films, sheets, laminates and molded articles, including monolayer and multilayer containers for barrier packaging. The compositions have thermal properties comparable with those of polyethylene terephthalate polymer and thus are well suited for manufacture of multiwall containers having excellent oxygen barrier and haze resistance properties. The oxygen barrier properties approach those of poly(metaxylyleneadipamide) and the compositions retain excellent clarity even when exposed to high humidity conditions.